A typical electrical transit vehicle includes propulsion equipment and various auxiliary apparatus that draw current from a power source third rail through pickup devices positioned at the front end of the vehicle and at the rear end of the vehicle. The provision of regenerative braking of that vehicle to stop the vehicle and supply power back into the third rail is described in an article entitled, "Alternative Systems for Rapid Transit Propulsion and Electrical Braking" by B. J. Krings, published in the March, 1973 Westinghouse Engineer. The resulting voltage across the line filter capacitor has been monitored to determine the receptivity of that third rail for such regenerative power such that if the capacitor voltage goes above a preset limit, then the regenerative braking is terminated and either dynamic braking or friction braking is used to stop the vehicle. The latter operation is disclosed in U.S. Pat. No. 3,657,625 of Miller et al. and assigned to the assignee of the present invention.
It is known in the prior art, as disclosed in U.S. Pat. No. 4,057,753 of R. H. Perry et al. to provide a permissive control signal which is inserted into the electrical power supplied to the vehicle for establishing when regenerative braking will occur and it is desired for the external power supply to receive regenerated power from the vehicle.